1) Field of the Invention
The present invention relates generally to seeding implements and, more specifically, to structure for providing constant and even down pressure on gangs of openers mounted on a relatively wide drill or similar implement.
2) Related Art
Seeding implements such as grain drills are manufactured with increasing widths for better productivity. Often, two or three drill sections are mounted on a carrier or are otherwise foldable for narrow transport. One problem has been maintaining a relatively constant down pressure on the furrow openers or other ground engaging tools across the width of the implement so that seeding depth remains uniform. As seed box weight changes and as irregular ground surfaces are encountered, the pressure and therefore the depth at which the tools operate can change substantially from one portion of the machine to the next, resulting in an uneven seed germination, inconsistent crop maturity and lower yields. When large obstacles such as rocks, stumps and the like are encountered, high loads may be experienced by a few of the tools.
To overcome problems associated with uneven ground conditions, flexible linkages on drill box carriers have been used. However, such linkages create complex mechanical design problems, and down pressure typically varies with the weight of the seed in the box.
Other arrangements to overcome surface irregularity problems and changing weight have included use of hydraulic cylinders. For example, U.S. Pat. No. 4,044,697 shows a hydraulic system wherein one cylinder is provided for each opener arm, and the cylinders are connected in a parallel circuit so an even amount of pressure is applied to each of the openers. Another parallel arrangement of hydraulic actuators for applying even down pressure to furrow-forming units is shown in U.S. Pat. No. 3,749,035. The individual cylinders, which add to the expense of the implement and require a considerable amount of plumbing, make such arrangements impractical for wide implements and implements with narrowly spaced openers. Uniform raising and lowering of the openers between the transport and ground working positions can also be a problem with use of a large number of parallel-connected cylinders.